Insulin and other injectable medications are commonly given with drug delivery pens, whereby a disposable pen needle assembly is attached to facilitate drug container access and allow fluid egress from the container through the needle into the patient.
As technology and competition advance, driving the desire for shorter, thinner, less painful, and more efficacious injections, the design of the pen needle assembly and parts thereof becomes more and more important. Designs need to proactively address ergonomically improving injection technique, injection depth control and accuracy, the ability to be safely used and transported to disposal, and protection against misuse while maintaining the ability to be economically manufactured on a mass production scale.
The assembly and operation to a typical drug delivery pen, as shown in FIGS. 1 and 2, is described in U.S. Patent Application Publication No. 2006/0229562, published on Oct. 12, 2006 and in U.S. Pat. No. 6,24,095, issued on Jun. 19, 2001, both of which are hereby incorporated by reference in their entirety.
Drug delivery pens, such as the exemplary pen injector 100 shown in FIGS. 1 and 2, typically comprise a dose knob/button 24, an outer sleeve 13, and a cap 21. The dose knob/button 24 allows a user to set the dosage of medication to be injected. The outer sleeve 13 is gripped by the user when injecting medication. The cap 21 is used by the user to securely hold the pen injector device 100 in a shirt pocket, purse or other suitable location and provide cover/protection from accidental needle injury.
FIG. 2 is an exploded view of the drug delivery pen 100 of FIG. 1. The dose knob/button 24 has a dual purpose and is used both to set the dosage of the medication to be injected and to inject the dosed medicament via the leadscrew 7 and stopper 15 through the medicament cartridge 12, which is attached to the drug delivery pen through a lower housing 17. In standard drug delivery pens, the dosing and delivery mechanisms are all found within the outer sleeve 13 and are not described in greater detail here as they are understood by those knowledgeable of the prior art. The distal movement of the plunger or stopper 15 within the medicament cartridge 12 causes medication to be forced into the needle 11 of the hub 20. The medicament cartridge 12 is sealed by septum 16, which is punctured by a septum penetrating needle cannula 18 located within the hub 20. The hub 20 is preferably screwed onto the lower housing 17, although other attachment means can be used, such as attaching to the cartridge. To protect a user, or anyone who handles the pen injection device 100, an outer cover 69, which attaches to the hub 20, covers the hub. An inner shield 59 covers the patient needle 11 within the outer cover 69. The inner shield 59 can be secured to the hub 20 to cover the patient needle by any suitable means, such as an interference fit or a snap fit. The outer cover 69 and the inner shield 59 are removed prior to use. The cap 21 fits snugly against outer sleeve 13 to allow a user to securely carry the drug delivery pen 100.
The medicament cartridge 12 is typically a glass tube sealed at one end with the septum 16 and sealed at the other end with the stopper 15. The septum 16 is pierceable by a septum penetrating cannula 18 in the hub 20, but does not move with respect to the medicament cartridge 12. The stopper 15 is axially displaceable within the medicament cartridge 12 while maintaining a fluid tight seal.
Intradermal drug delivery has provided many clinical advantages, from vaccine delivery to insulin delivery. An intradermal drug delivery is made by delivering the drug into the dermis layer of the skin. However, a higher injection pressure, up to 200 psi or higher, is occasionally needed to overcome back pressure from intradermal tissue, because it is not as soft as subcutaneous tissue, which is mainly fat tissues. To facilitate self-injection, a lower back pressure and smaller amount of force is preferred to make the injection. Thus, a need exists for a drug delivery pen that amplifies the input force to facilitate an intradermal medication injection.
The backpressure in subcutaneous injections is not very large, while the backpressure associated with intradermal injections may be many times greater than that of subcutaneous injections. For example, the backpressure often exceeds 200 psi for an intradermal injection, while the backpressure for a subcutaneous injection is generally in the range of 30-50 psi. Thus, a need exists for a drug delivery pen that has a high mechanical gain to reduce thumb forces required to overcome the initial high breakout force in the cartridge during an intradermal injection.
Existing drug delivery pens have limited mechanical advantage due to the requirements of subcutaneous delivery, which has a relatively low backpressure. However, as noted above, the backpressure associated with intradermal injections is substantially higher. Therefore, the drug delivery pen should have a much larger mechanical gain to allow a user to apply a comfortable thumb force, and to gain it up to a higher force on the cartridge stopper. However, the higher force is preferably needed during the first stage of the injection, i.e., the breakout force. After the initial breakout, the injection force is reduced to a significantly lower level and is substantially constant through the end of the injection.
Existing methods of performing high pressure injections use high pressure gas or strong springs to generate a high pressure to drive the plunger. However, such methods make it difficult to achieve a slow injection. Moreover, such methods have high manufacturing costs, which is not desirable for routine self-injections, such as insulin self-injections. Another method used is a triple start thread design to generate required constant force amplification. However, such generated force is not sufficient for an intradermal delivery force and also reduces the total dose range. Additionally, there are no existing devices that can be used with existing drug delivery pens to generate the required push force at the leadscrew with a reasonable thumb force being applied.
Accordingly, a need exists for a pen needle assembly for a drug delivery pen that facilitates intradermal medication injection.